The present invention relates to optical instruments and can be particularly used to develop new and improve existing devices for analysis of a surface of semiconductor wafers, and to integrate the devices into the manufacturing equipment, as well as to examine the uniformity degree of a surface of other articles.
During the manufacture of semiconductor devices, no dust particles and other defects can be tolerated on the surface of semiconductor wafers. It is desirable to reveal such defects as early as possible to remove at once a source of their origin. To solve this problem a method is widely used utilizing the known fact that any particle on a smooth surface, or a surface defect scatters the light incident onto the surface.
For example, a method for inspection of an analyzed surface is known from U.S. Pat. No. 4,314,763 (Int.Cl. G 01 N 21/88, 09.02.82), comprising the steps of: rotating the analyzed surface about a center of rotation, forming a light spot on the analyzed surface, and sensing a light scattered from the analyzed surface using an optical system.
The same U.S. Pat. No. 4,314,763 discloses a surface scanning analyzer comprising: a light source for illuminating an analyzed surface by a light spot at an angle close to the normal to the analyzed surface; a photodetector for sensing the light scattered from the analyzed surface; and a rotary table for mounting and rotating an article with the analyzed surface thereon about an axis of revolution parallel to the normal to the analyzed surface.
In the analyzer implementing the above method, the rotated analyzed surface is being moved along a straight line relative to a point at which the light spot is formed on the surface. This is the shortage of the method and the analyzer implementing the method since it is necessary to provide movement of a large object, i.e. the rotary table for mounting a semiconductor wafer (up to 300 mm in diameter), equipped with a rotation actuator, which leads to increased size and cost of the device.
The closest prior art is a method for inspection of an analyzed surface comprising the steps of rotating an object having the analyzed surface about a first center of rotation; forming a light spot on the analyzed surface sensing a light scattered from the analyzed surface at the incidence point of the light spot (Altendorfer H. et al.  less than  less than Unpatterned surface inspection for next-generation devices greater than  greater than .xe2x80x94Solid State Technology, 1996, v. 39, No 8, pp. 93-97).
The same reference discloses a surface scanning analyzer comprising: a rotary table for mounting and rotating an object with an analyzed surface about a first axis of revolution that is perpendicular to the analyzed surface; a light source for illuminating the analyzed surface by a light spot at an angle close to the normal to the analyzed surface; a collecting mirror in the form of a truncated body of revolution formed by revolving an ellipse about a second axis of revolution which is parallel to the first axis of revolution and substantially coincides with the normal to the analyzed surface erected at the incidence point of said light spot, said incidence point being at the focus of said truncated body of revolution, a first section plane of the body of revolution being perpendicular to the second axis of revolution in the immediate proximity to said focus, and a second section plane being parallel to the first section plane; a photodetector for sensing the light scattered from the analyzed surface and reflected from the collecting mirror.
In this method a progressive movement of the rotated analyzed surface is remained, i.e. as before it is necessary to move a massive object, which results, as mentioned before, in increased size and cost of the device, hampering substantially integration of the device into the process equipment.
Recent developments of a cluster type equipment in the semiconductor industry have enabled several operations to be carried out simultaneously and ensured the cleanness grade infeasible with conventional equipment. The appearance of new process equipment poses the problem to develop a new measurement equipment capable of operating in the cluster process conditions. The demands imposed on such devices differ significantly from the demands placed on conventional devices. One of the most important requirements is a minimal size of the device, which is dictated by a small volume of clean environment inside the cluster. module. Since the cluster measurement devices are integrated into each individual module, they must be also manufactured and serviced at a low cost.
Thus, the object of this invention is to develop such methods for inspection of an analyzed surface, and a surface scanning analyzer that would be free from the indicated drawbacks.
The above object and the indicated technical result of the present invention are achieved in the following manner.
In one aspect, the invention relates to a method for inspection of an analyzed surface, comprising the steps of: rotating an object having the analyzed surface about a first center of rotation; forming a light spot on the analyzed surface; sensing separately a light mirror-reflected and a light scattered from the analyzed surface at the incidence point of the light spot, wherein in accordance with the present invention, the method includes the steps of: moving the light spot relative to the analyzed surface through an arc about a second center of rotation which lies outside the analyzed surface; and aligning, at least in one predetermined position, the light spot having an elongated form on the analyzed surface with its maximum size along a radius extending from the first center of rotation through the light spot.
A feature of this method is that in the predetermined position the light spot is located substantially in the middle of said analyzed surface radius extending from the first center of rotation, or the light spot, during its movement through said arc, is turned so as to retain its alignment along the radius extending from the first center of rotation thought the light spot all along the scanning line.
One more feature of this method is that the light scattered from the analyzed surface is collected using a system of mirrors, wherein one of the mirrors is in the form of a truncated ellipsoid of revolution having one axis of revolution substantially coinciding with the normal to the analyzed surface erected at the incidence point of said light spot, said incidence point being at a first focus of said truncated ellipsoid of revolution, a first section plane of the ellipsoid being located perpendicularly to its axis of revolution in the immediate proximity to said first focus, and a second section plane being parallel to the first section plane, and another mirror is a flat mirror having an aperture at the center, arranged at an angle to the axis of revolution of the truncated ellipsoid of revolution, and intended for passing therethrough the light from the light source to the analyzed surface and the light mirror-reflected therefrom, and for reflecting the light scattered from the analyzed surface and reflected from the collecting mirror, wherein the light reflected from the flat mirror is passed through a light filter and then diaphragmed at a point corresponding to the second focus of said ellipsoid of revolution with regard of reflection from said flat mirror.
In one embodiment of the method, the light scattered from the analyzed surface is collected using a system of mirrors, wherein one of the mirrors is in the form of a truncated paraboloid of revolution having an axis of revolution substantially coinciding with the normal to the analyzed surface erected at its incidence point of said light spot, said incidence point being at the focus of said truncated paraboloid of revolution, a first section plane of the paraboloid being located perpendicularly to the axis of revolution in the immediate proximity to said focus, and a second section plane being parallel to the first section plane, and another mirror is a flat mirror having an aperture at the center, arranged at an angle to the axis of revolution of the truncated paraboloid of revolution, and intended for passing therethrough the light from the light source to the analyzed surface and the light mirror-reflected therefrom and for reflecting the light scattered from the analyzed surface and reflected from the collecting mirror, wherein the light reflected from the flat mirror is passed through a light filter, collected by a lens and then diaphragmed.
In another aspect, the present invention relates to a surface scanning analyzer comprising: a rotary table for mounting thereon an object with an analyzed surface, and rotating the same about a first axis of revolution that is perpendicular to the analyzed surface; a light source for illuminating the analyzed surface by a light spot at an angle close to the normal to the analyzed surface; a collecting mirror in the form of a truncated body of revolution formed by revolving a second order curve about a second axis of revolution which is parallel to the first axis of revolution and substantially coincides with the normal to the analyzed surface erected at the incidence point of said light spot, said incidence point being at the focus of said truncated body of revolution having a first section plane perpendicular to the second axis of revolution in the immediate proximity to said focus, and a second section plane parallel to the first section plane; a first light sensing unit for sensing the light mirror-reflected from the analyzed surface, located close to the light source; a second light sensing unit for sensing the light scattered from the analyzed surface and reflected from the collecting mirror; a flat mirror having an aperture at the center, arranged at an angle to the axis of revolution of the truncated body and intended for passing therethrough the light from the light source to the analyzed surface and the light mirror-reflected therefrom to the first light sensing unit and for reflecting the light from the collecting mirror to the second light sensing unit, wherein in accordance with the present invention, the light source, the collecting mirror, the flat mirror with the aperture, and the first and second light sensing units are accommodated in a housing rotatable about a third axis of revolution which is parallel to the first axis of revolution and passes outside the object with the analyzed surface and/or the rotary table; the light source is mounted so as said light spot having an elongated form on the analyzed surface is aligned, at least in one predetermined position, with its maximum size along a radius extending from the first center of rotation through the light spot.
A feature of this analyzer is that the first light sensing unit is a light absorber or a photodetector to determine the presence of non-scattering defects on the analyzed surface.
Another feature of this analyzer is that the second light sensing unit is intended for sensing the light reflected from the flat mirror.
One more feature of this analyzer is that the body of revolution of the collecting mirror is an ellipsoid of revolution having a diaphragm placed at the second focus with regard of reflection from the flat mirror, for passing through the diaphragm the light reflected from the flat mirror to the second light sensing unit. In this case, a light filter may be mounted between the flat mirror and the diaphragm.
A feature of another embodiment is that the body of revolution of the collecting mirror is a paraboloid of revolution, and a collecting lens and a diaphragm may be mounted between the flat mirror and the second light sensing unit, for collecting and passing the light reflected from the flat mirror to the second light sensing unit. In this case, a light filter may mounted between the flat mirror and the collecting lens.
One more feature of the analyzer is that it further comprises a housing rotation actuator to enable movement of the housing over the analyzed surface at least to one side from the center of rotation.
Yet one more feature of the analyzer is that in said predetermined position of the housing, said light spot is located substantially in the middle of said analyzed surface radius extending from the center of rotation of the surface, or in that the housing rotation actuator is provided with housing rotation angle measurement means, and the light source is provided with position correction means for turning the light source in accordance with signals from the rotation angle measurement means to enable said aligning of the light spot along the radius extending from the center of rotation of the analyzed surface all along the scanning line.
Yet one more feature of the analyzer is that the housing is light-absorbing on the inside.
At last, one more feature of the analyzer is that the rotary table is provided with three suction cups located symmetrically about the first axis of revolution and intended for mounting the object with the analyzed surface on the rotary table.
No objects of the same purpose as the claimed ones, which would possess all of the aforementioned features of the subject matters of the present invention, have been revealed in the background art. Thus, the method for inspection of an analyzed surface and the surface scanning analyzer in accordance with the present invention may be considered novel.
Subject matters of the same purpose as the claimed ones are known, which comprise individual features similar to the main features of the claimed method and analyzer. For example, in U.S. Pat. Nos. 5,377,001 and 5,377,002 (Int.Cl. G 01 N 21/00, 27.12.94), the light spot is shown on the analyzed surface (FIG. 7a in each of these patents) in an elongated form along the radius extending from the center of rotation of the analyzed surface; however, the specifications to the patents lack any explanations as to how the spot should be arranged throughout the scanning line. Moving the analyzed surface in two mutually perpendicular directions is disclosed in EP Application No 0398781, Int.Cl G 01 N 21/88, 22.11.90. Linear movement of the assembly with the light source and a light sensing unit over the rotary analyzed surface is known from Japan Unexamined Application No. 03-163338 (Int.Cl. G 01 N 21/88, 15.07.91). The use of a rotary housing in the form of the tone arm is known as such in disk turntables. RU Patent No. 2064670 (Int.Cl. G 01 N 21/47, 27.07.96) teaches the use of the collecting mirror in the form of the ellipsoid of revolution. However, no information is available in the background art on the use of a rotary housing for placing therein optical elements to illuminate the analyzed surface and sense light fluxes mirrored and scattered therefrom, as well as information on how the light spot must be just aligned on the analyzed surface. Thus, the subject matters of the present invention may be considered involving the inventive step.